In 1902 in the disease-ridden Pontine Marshes, a disease-ridden region, 12-year-old Maria Goretti lives with her parents, poor farmhands, in the house of Serenelli, a heavy-drinking farmer who offered them board and lodging. Serenelli's 18-year-old son Alessandro is sexually attracted to the pious Maria, who resists his advances. One day the young man murders her because she won't give in to him. Before she dies, Maria forgives her assailant. After her death she is canonized as a saint.